The present invention relates to a method of performing heat treatment on a high-molecular film, especially a roll film having knurled portions in both side edges.
A high-molecular film, especially a polyester film, is subjected to heat treatment in order to remove its residual distortion which has been sustained in the process of production thereof. This is called annealing treatment. For this annealing treatment, a method in which a wound roll film is preserved in a high-temperature isothermal chamber for a time longer than a predetermined time or a method in which a wound roll film is treated in a continuous furnace at a low speed is carried out. If the roll film is heated unevenly in this process, there arise a problem of tightening, creasing and weaving in winding state in connection with the winding core, and another problem such as long time preservation of the wound roll film, and so on.
To make a measure against those problems, there are a method (1) in which to relax the influence of the winding core, a film having a thermal expansion coefficient not larger than the wound film is wound under on the winding core and annealing treatment is performed on the whole (see Japanese Patent Unexamined Publication No. Hei-4-247321), an apparatus (2) in which dielectric heating is used as a heating method at the time of winding in production so as to cope with gradual increase of the diameter of the wound roll so that heating is carried out at an equal distance from the roll surface, and, in addition, the winding pressure is adjusted (see Japanese Patent Examined Publication No. Sho-52-14451), a method (3) in which a wound roll film is heated in a heating furnace in a state that a spacer is put between both edge portions of the film before winding, and then the film is preserved in the heating furnace for a predetermined time after winding (see Japanese Patent Examined Publication No. Hei-5-19899), and so on.
The method described in Japanese Patent Unexamined Publication No. Hei-4-247321, however, requires a surplus of under winding, so that there are disadvantages in equipment, material and working. The apparatus described in Japanese Patent Examined Publication No. Sho-52-14451 requires expensive and complex equipment. The method described in Japanese Patent Examined Publication No. Hei-5-19899 is insufficient in its effect against creasing, weaving, etc. in the winding state because a gap is interposed between the spacer and the film so that air between film layers is leaked.
An object of the present invention is to solve the aforementioned problems and to provide a method of performing heat treatment on a wound roll film in which annealing treatment can be carried out in bulk so as to obtain a sufficient effect against creasing, weaving, etc. in the winding state without the necessity of surplus equipment, material, working, etc. and without the necessity of complex equipment.